This invention relates to a dielectric ceramic composition for a multi-layer capacitor comprising internal electrodes mainly containing Cu or Cu alloys and dielectric layers mainly containing Pb based perovskite ceramics, particularly relates to a composition having a small temperature coefficient of capacitance which is in the range of Y-class B-characteristic of JIS (Japanese Industreal Standard) which has the temperature change ratio variation from -25.degree. C. to 85.degree. C. within .+-.10% based on a value of 20.degree. C.
Recently, multi-layer capacitors have been mainly used in the electric circuits of various electric products to meet need of small-sized and large-capacitance capacitors. Such multi-layer capacitors are usually made by co-sintering internal electrodes and dielectric ceramic body. Conventionally a ceramic composition comprising barium titanate system is widely used as dielectric materials for a ceramic capacitor having a high dielectric constant. However, since such barium titanate ceramics are sintered at a temperature as high as about 1300.degree. C., it is required to use metals such as Pd, Pt and the like which have a high cost and a high electric resistance, for internal electrodes of multi-layer capacitors. Further, owing to inferiority in DC bias and signal voltage characteristics, dielectric layers of barium titanate ceramics can not get thinner in order to make a capacitor small-sized and have large capacitance.
Therefore, a multi-layer capacitor comprising internal electrodes made of Cu having a low cost and a low electric resistance and dielectric layers made of Pb based perovskite ceramics having a good voltage characteristic and a low sintering temperature is strongly desired. There has also been proposed a dielectric ceramic composition which has practical electric characteristics and is able to be sintered together with Cu, that is, sintered under a condition in which Cu can not be melted or oxidized. Furthermore, we have proposed a method by which the above multi-layer capacitor can be mass-produced. Therefore, a multi-layer capacitor having a good commercial cost and larger capacitance although it is small-sized, is realized so that electrolytic capacitors can be replaced by the multi-layer capacitors.
However, the multi-layer capacitor proposed up to the present time has a poorer temperature coefficient of capacitance (corresponding to JIS Y E characteristic), so that thus produced capacitor can be used only to a limited extent. Therefore, it is desired to develop a superior capacitor has large capacitance which meet the above Y B-characteristic which has the temperature change ratio from -25.degree. C. to 85.degree. C. within .+-.10% based on a value of 20.degree. C. However, there has not been yet developed a capacitor having a practical level in CR product, voltage characteristic and the like.